The present invention relates to a multicomponent measuring wheel.
A multicomponent measuring wheel is described in German Patent No. 41 33 418 C2. The multicomponent measuring wheel described is integrated in a vehicle wheel for measuring purposes and offers the advantage of being able to be installed on different vehicles without requiring significant retrofitting. The actual sensor part, which is coupled to a wheel rim that supports the vehicle tire, is made of a ring of a plurality of stud bolts running in parallel to the wheel axle, and of an essentially star-shaped measuring disk, which includes eight radially running segments joining an inner ring and an outer ring of the measuring disk. Besides securing the measuring disk to an auxiliary flange attached to the wheel rim, the stud bolts act as axial measuring cross-sections and are fitted with strain gauges. The radially configured, spoke-like segments are used as measuring segments, and are likewise fitted with strain gauges. This arrangement facilitates the measuring of force components in the x-, y- and z-direction, as well as of their corresponding moments. The drawback of this multicomponent measuring wheel is that it is made of many individual parts, so that its assembly must be as tolerance-free as possible, and is therefore time-consuming and expensive.
German Patent No. 44 30 503 C1, describes a torque sensor having a strain gauge configuration, whose measuring body is formed from an annular region of a disk member situated in an axial plane. The disk member includes a first torque transmitting part radially adjoining the measuring body region to the inside, and a second torque transmitting part radially adjoining the measuring body region to the outside; one of these constituting the torque-introducing and the other the torque-delivering side for the measuring body region. The annular region has a smaller axial thickness than the torque transmitting parts, so that it exhibits mechanical stresses in response to the action of torque. This torque sensor is suited for determining torques in motor-vehicle gear units.
A multicomponent measuring wheel that has sensors located between the wheel-rim face and a wheel flange is described in German Patent Application No. 43 11 903 A1, the wheel flange and/or the rim face being made from a fibrous composite material. Wheel-side energy- and data-transmission means are mounted on the inner side of the rim well, which accommodates a vehicle tire, and extend essentially over its circumference. The connection between the rim well and the rim face is achieved by fabricating the fibrous composite material for the rim face in the previously sandblasted rim well, thus producing a positive-locking connection characterized by good adhesive power. In the case of the known measuring wheel, this refinement eliminates the need for an energy/data transmission system that projects over the outside lateral contours of the vehicle and for a retaining frame that would otherwise be required for it. However, this refinement entails a rim-specific adaptation, so that the known measuring wheel is not suited for use with other rims.
German Patent No. 42 16 670 C2 describes another multicomponent measuring wheel whose radial/tangential connection arrangement rigidly joins the wheel hub in the radial and tangential directions of the measuring wheel to the rim and, in the axial direction, acts as a soft connection -between the hub and the rim, the stiffness of this connection arrangement differing in the radial and tangential directions. This type of construction would be susceptible to faults due to its relatively non-compact construction.
These prior measuring wheels have the disadvantage of entailing high costs in the manufacturing and installation of the measuring wheels, because of the multiplicity of individual parts. In addition, a large number of strain gauges is needed, so the result is considerable expenditure for applications and wiring. Moreover, an unfavorable ratio can be established between the maximum material stresses and the useful stresses for the strain gauges.
An object of the present invention is to provide a multicomponent measuring wheel having a measuring element located between a hub and a wheel rim, the measuring element having a small type of construction in the axial direction, i.e., protruding to a relatively small extent out of the wheel plane formed by the hub and the rim.
The present invention therefore provides a multicomponent measuring wheel having a rim (1, 31), a hub (15), and a measuring element (2) arranged between the rim (1, 31) and the hub (15), and having a strain gauge arrangement (9, 10), wherein the measuring element (2) is substantially rotationally symmetric with respect to the axis of rotation of the multicomponent measuring wheel and is designed as a one-piece element.
In accordance with the present invention, a multicomponent measuring wheel having a compact type of construction is provided for measuring forces and torques acting between a hub and a rim. The multicomponent measuring wheel has a very small type of construction, i.e., it protrudes only slightly from the wheel plane formed by the hub and the rim. A multicomponent measuring wheel of this kind is suited for use on a test stand, as well as under conditions of everyday life, such as in street traffic. Since the measuring element is designed as a one-piece element and is rotationally symmetric, it can be easily installed between the hub and the rim. The expenditure for assembly is reduced as compared to conventional measuring arrangements having a plurality of individual parts. The measuring element of the present invention, as well as the rim and hub, are modular components, which can be simply replaced, when needed, on an individual basis.
According to one preferred specific embodiment of the invention, the measuring element has an annular flange, which is attached to the rim and extends essentially radially to the inside; a tubular section adjoining this flange radially to the inside and extending essentially axially; an intermediate flange adjoining the tubular section radially to the inside; an annular region adjoining the intermediate flange radially to the inside; and an annular flange adjoining the annular region radially to the inside and attached to the hub, if indicated via at least one hub adapter. A measuring element of this kind is simple to manufacture in one piece and proves to be very rugged in practice. At the same time, a low level of material stress is ensured, while a high measuring sensitivity is maintained. In this case, the essentially axially extending tubular section, and the essentially radially extending, annular region 7 are used as measuring cross-sections, which are fitted in a generally known manner with the strain gauges, which will be discussed in greater detail further below. Therefore, by uniformly distributing strain gauges of this kind, one can eliminate load-dependent changes in resistance, so that exclusively those changes in resistance that are conditional upon torque are outwardly effective. By suitably configuring the strain gauges, the corresponding useful signals are optimized, while spurious signals are simultaneously minimized. Regarding the various possibilities for wiring strain gauges in this manner, reference is made, for example, to German Patent No. 27 08 484 C2. In contrast to the remaining regions of the measuring element, the sections conceived as measuring cross-sections exhibit relatively little stiffness, so that strains that occur can be effectively used to divert measuring signals.
Expediently formed in the interconnecting region between the tubular section and the intermediate flange is an axial undercut groove, i.e., an axial notch. In this way, the overall axial length of the multicomponent measuring wheel can be further reduced.
According to one preferred embodiment of the multicomponent measuring wheel of the present invention, the axial thickness of the annular region of the measuring element diminishes in the radial direction from the inside to the outside. Therefore, in response to the action of forces or moments, a uniform stress distribution in the radial direction in the annular region is obtained, thus simplifying the evaluation of measuring signals from strain gauges installed there.
The intermediate flange expediently has a radially inwardly directed annular shoulder, or step, region. A shoulder region of this kind is relatively protected from external influences, so that solder tags are able to be advantageously applied in this region.
The strain gauges are advantageously arranged on the annular region, in particular on its axial inner and outer partitions, and/or the tubular section, in particular its inner side. The stiffness of these regions is relatively slight, so that exact measurements are able to be performed.
The strain gauges each advantageously cover an angular range of 20xc2x0 to 40xc2x0. When strain gauges of this kind are used, measuring signals of sufficient amplitude are easily obtained. In addition, fewer strain gauges are needed to attain a sufficiently accurate measurement, as compared to conventional arrangements, so that the outlay for wiring is reduced.
In expedient fashion, the strain gauges of the strain gauge arrangement are wired into full or half bridge circuits. This generally known wiring enables any strain experienced by the multicomponent measuring wheel to be converted into electrical voltage.
According to one advantageous embodiment, the tubular section has an inner conically formed, and an outer cylindrically formed section. This ensures a rugged connection to the radially outer flange, as well as relatively little stiffness for the region of the tubular section, upon which the strain gauges are mounted.
The tubular section advantageously has a diameter/length ratio of less than 1:6. By conforming to these dimensions, a small axial overall height is achieved, while adequate sensitivity is maintained for the measuring element.
Provision is expediently made inside the multicomponent measuring wheel, in particular inside the tubular section, for transmitting components for transmitting recorded measuring signals to an evaluation device. By utilizing the interior space of the tubular section, one can achieve a very compact type of construction for the multicomponent measuring wheel.
It is preferred that the measuring element be attachable by using centering shoulders, or steps, and/or positioning pins, in particular by using at least one hub adapter that is able to be connected to the hub, as well as to the wheel rim. Because connections of this kind are simple to manipulate, the expenditure for assembling the multicomponent measuring wheel is reduced and replacement of the individual parts is facilitated.